This invention relates to an acceleration sensor which has a pair of sensor units capable of being put together into two different assemblies being symmetrical in shape with each other, and a safety belt retractor incorporating the same sensor.
Conventionally, safety belt retractors are known which are provided with a locking device which is sensitive to abnormal acceleration or inclination of the vehicle in an emergency and locks a takeup shaft on which a webbing is wound, against rotation to prevent unwinding of the webbing. Some retractors of this type employ acceleration sensors using ball weights as inertia means in order to sense acceleration or inclination of the vehicle. In most sensors of this type, the ball weight is moved in response to acceleration of the vehicle above a certain magnitude or inclination of the vehicle above a certain angle, to actuate the locking device. To ensure proper functioning of the acceleration sensor of this type, it is an essential requisite that the sensor, e.g. its ball weight, should be positioned so as to function without fail when a predetermined emergency condition is fulfilled.
However, in vehicles such as automobiles in which safety belts are widely used, if a retractor for a right-side occupant's seat, which is designed to be inclined forwardly downward when it is mounted in the vehicle, is used at a left-side occupant seat, it has to be inclined rearwardly downwardly when it is mounted at the left-side occupant's seat, failing to properly function in an emergency. Therefore, two kinds of retractors have to be provided for use at the right-side and left-side seats, respectively. Further, the sensor and the retractor body have to be designed in two different shapes for respective use at the right-side and left-side occupant's seats so as to properly function upon fulfillment of the predetermined emergency condition. That is, the sensor and the retractor body are required to have different component parts between the right-side seat and the left-side seat, which renders their mounting into the vehicle complicated, and causes increased costs.